JP2002264152A - Method for manufacturing film and protective film for polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably manufacturing a smooth film for a long time by which deposits, etc., on the surface of a substrate can be suppressed while good releasing properties are kept in the method for manufacturing the film by which a polymer solution is cast and molded on the substrate. SOLUTION: In the method for manufacturing the film by which the polymer solution is cast and molded on the substrate, the method for manufacturing the film characterized by providing a continuous spiral channel on the surface of the substrate is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polymer solution cast film using an endless belt or drum as a support.

[0002]

2. Description of the Related Art In a solution casting film forming method in which a polymer solution is cast on a support such as a drum or an endless belt,
The smoothness of a film used for optical applications is important.

[0003] In order to obtain a film having such a smooth surface, it is necessary that the support is smooth, and it is desirable that the support has a high surface hardness, excellent corrosion resistance, and is mirror-finished. Plated or stainless steel with excellent corrosion resistance and workability is used.

In order to obtain a support having a smooth surface, a material having a small amount of impurities is sufficiently polished in a clean environment from which foreign substances and the like are removed as much as possible to obtain a mirror surface. For example, JP-A-2000-84
As described in JP-A-960, by setting the center line average roughness Ra of the support surface to 1 to 3 nm, the roughness of the film surface and the haze value of the film are prevented from increasing.

[0005] The smoothness of the film formed by the solution casting film forming method becomes better as the amount of foreign matter and unevenness on the surface of the support is smaller.

[0006] However, the smoothness of the formed film is affected not only by the flatness of the surface of the support but also by the releasability when peeled from the endless belt or drum. In the case where the peelability of the film from the drum is poor, a substantially linear film deformation in the width direction may occur continuously at substantially equal intervals in the transport direction on the film surface after peeling. This deformation of the film surface does not occur in the initial stage of using a flat polished support, but it tends to occur over time if the film formation is repeated, and deposits from the film and the support It is considered that a substance generated by a chemical reaction or the like on the surface gradually accumulates to form surface irregularities, thereby deteriorating the releasability.

[0007] Precipitates and the like that accumulate due to repeated film formation are reduced as the surface of the support is closer to the mirror surface. Conversely, when the surface of the support is closer to the mirror surface, the adhesion to the cast film is increased, and the separation is caused. May deteriorate.

[0008] Therefore, it has been practiced to improve the releasability by forming a mat-like unevenness after once processing the entire surface into a sufficient mirror surface, but by forming the mat-like unevenness on the surface, Precipitates tend to accumulate,
For that purpose, cleaning and rework of the surface of the support are frequently required.

[0009]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above problems, and has a method for producing a film by casting a polymer solution on a support to maintain good releasability. An object of the present invention is to provide a method for producing a smooth film stably for a long period of time while suppressing accumulation of precipitates and the like on the surface of a support.

[0010]

The above object of the present invention has been attained by the following means.

1. What is claimed is: 1. A method for producing a film, comprising casting a polymer solution on a support and forming the film, wherein a continuous spiral groove is provided on the surface of the support.

2. 2. The method for producing a film according to the above item 1, wherein the support is an endless belt.

3. 2. The method for producing a film according to the above item 1, wherein the support is a drum.

4. The method for producing a film according to any one of the above items 1 to 3, wherein the maximum diameter of the spiral formed on the surface of the support is 500 mm or less.

[0015] 5. In the continuous spiral groove formed on the surface of the support, the distance (pitch) between adjacent grooves in the width direction of the support is 10 mm or less.
5. The method for producing a film according to any one of 4.

6. On the surface of the support, a plurality of spiral grooves formed continuously in the width direction are formed in the transport direction, and the grooves formed at positions shifted in the transport direction have at least a shared area with each other. The film production method according to any one of the above 1 to 5.

[7] The method for producing a film according to any one of the above items 1 to 6, wherein the depth of the continuous spiral groove on the surface of the support is 1 to 5 nm.

[8] Wherein the polymer solution is a cellulose ester solution, and the film thickness of the formed cellulose ester film is 20 to 200 μm.
The method for producing a film according to any one of the above items.

9. A protective film for a polarizing plate, comprising a cellulose ester film formed by the film production method of the above item 8.

In the production of a film in which a polymer solution is cast on a metal support (belt or drum) to form a film, a polymer solution (sometimes called a dope) is flowed on a metal support (belt or drum). It comprises a casting step, a drying step on a metal support, and a peeling step of peeling the web from the metal support. The surface of the metal support is usually a mirror surface, and in the casting step, the dope is fed to a pressure die through, for example, a pressure-type fixed gear pump, and at the casting position, an endless metal belt or a rotating endless transition. This is a step of casting a dope from a pressure die onto a metal support of a metal drum.

In the present invention, the surface condition (irregularity) of the belt or drum used for film forming is changed not by a flat polished mirror surface from which the above foreign substances are removed as much as possible but by a pitch of a certain size on the surface. By providing certain surface characteristics, surface irregularities due to accumulation of precipitates and the like on the surface of the metal support are reduced (the need for frequent cleaning and reworking of the support surface is reduced), and casting is also performed. It has been found that it is possible to obtain a film forming method capable of stably obtaining a film having excellent peelability and excellent smoothness for a long period of time.

In the present invention, a metal support (endless belt, drum, etc.) used for film formation by a casting method
This is achieved by applying a constant pitch of scratches (grooves having a certain depth) at a constant density per unit area so as not to affect the surface properties (optical properties) of the formed film.

When the surface is matted as described above,
Although the releasability is improved, the accumulation of precipitates is likely to occur due to the formation of minute irregularities on the surface, and conversely, the closer the film is to a completely smooth mirror surface, the more the problem of the releasability of the formed film occurs. As a result, a problem arises that a precipitate is easily generated during repeated film formation.

The aforementioned fixed-pitch flaws (grooves having a certain depth) on the surface of these belts or drums are limited as long as the depth of the grooves is controlled so as not to affect the optical properties of the film. The shape is not particularly limited, and the number per unit area is not limited as long as the deterioration of the surface state due to accumulation of the precipitate is not remarkable. Considering a good workability method for randomly giving a state, it is preferable to use the continuous spiral (coil-shaped) groove.

Therefore, in the present invention, in a method for producing a film in which a polymer solution is cast on a support, a continuous helical groove is provided on the surface of the support so that stable peeling can be performed for a long period of time. That is, you can get the character.

Hereinafter, the continuous spiral groove and the method of forming the groove will be described in detail. Normally, a polisher that performs polishing by rotating a polishing pad is used for surface processing (polishing) of a support (endless belt or drum) for film casting. In the present invention, the polisher is used to control a polishing pad and an abrasive so that these drums and endless belts can be mirror-finished in place of a certain random continuous spiral (coil) according to the present invention. Can be provided on an endless belt or drum for casting. Hereinafter, a method of processing the above-described belts or drums with grooves having a constant pitch and processing the grooves with a substantially constant number (at a density) per area will be described.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram schematically showing a state of surface micro-deformation (irregularity) generated on a film surface when the above-mentioned peelability is poor. It can be seen that a number of streak-like deformations (represented by a number of straight lines in the width direction of the film in the figure) are generated substantially over the entire width of the film so as to be substantially orthogonal to the transport direction. Conventionally, methods such as appropriately matting the surface have been used in order to increase the releasability, but minute irregularities occur over the entire surface of the casting (casting) support (endless belt or drum). At present, it is difficult to find conditions satisfying both the peelability and the deposition of foreign matter.

In the present invention, therefore, the surface of the support such as the belt or drum for casting is formed by forming grooves of a certain depth with an appropriate interval substantially uniformly over the entire surface of the belt or drum.
An object of the present invention is to provide a method of forming a film that simultaneously satisfies both the above-mentioned releasability and the deposition of foreign matter.

The effect is that these grooves are present at a certain depth and with a certain degree of randomness over the entire surface of the belt.

For example, it is not always necessary to have a fixed form. For example, a rectangular or other form of a scratch having an appropriate size or a straight line or curve of an appropriate length is randomly formed over the entire surface of the endless belt. Alternatively, two sets of straight lines that cross each other may form regular scratches on the entire surface. However,
It is difficult to efficiently generate a pattern consisting of the above-mentioned flaws of a certain cycle over the entire surface of the belt, and a flaw of an appropriate depth is formed over the entire surface of the endless belt for casting at an appropriate cycle. Preferably, the continuous spiral groove as in the method according to the present invention is preferable from the viewpoint of ease of belt surface processing and the reliability of the effect.

In the present invention, usually, a polisher of a type for rotating a polishing pad used for mirror-finishing a belt or a drum used for these castings is used, so that the polisher can be efficiently and appropriately cycled at an appropriate period. Scratches with rough depths are roughened.

FIG. 2 shows an example of a support having a continuous spiral groove formed on the surface of the support when the support is an endless belt according to the method of the present invention. A continuous spiral (coil) -shaped groove is formed periodically (not necessarily at a fixed period) in the width direction of the belt corresponding to the width direction of the film, at a certain pitch (represented by P in FIG. 2). ing. The size of the helix also need not be a loop of exactly the same size in each period, but the maximum diameter of the helix loop (represented by D in the figure) is 500 mm, preferably between 300 and It is 500 mm, more preferably in the range of 200 to 300 mm. If it is more than this, the releasability will be deteriorated, and it will be close to the characteristics of the mirror surface. By setting the maximum diameter of the spiral groove formed on the support surface to 500 mm or less, uniform peelability can be obtained over the entire surface. In addition, a spiral groove having an excessively small diameter deteriorates the releasability, and a length of 100 mm or more is required to keep the releasability at a good level and to reduce the deposition of deposits on the drum. Preferably 20
The range is 0 to 300 mm.

The period of the helix need not be exactly the same with each period, but the interval (pitch (P)) between adjacent grooves of the helix should be 10 mm or less. By setting the interval (pitch) between the continuous spiral grooves to 10 mm or less, partial peeling force variation is eliminated, and uniform peelability can be obtained. On the other hand, if it is too small, the groove becomes almost continuous and the effect of the present invention cannot be obtained. Therefore, the lower limit is about 0.2 mm, and preferably 0.3 mm or more.

The depth of the groove is preferably in the range of 1 to 5 nm, whereby the accumulation of precipitates and the like can be suppressed for a long period of time while maintaining the releasability. If the depth of the groove is deeper than this, on the contrary, the releasability deteriorates, the accumulation of precipitates and the like also increases, and it is clearly observed as step unevenness on the formed film, and the optical properties Also gets worse. If the depth is smaller than this, the effect of the present invention cannot be obtained.

Preferably, a plurality of these continuous spiral (coil) -shaped grooves cut in the width direction of the support are provided in the transport direction, and are cut in the width direction of the support. In each of the plurality of continuous spiral (coil) -shaped grooves, it is necessary that the interval (pitch) between the grooves in the width direction is equal to or less than the above-described distance and that the grooves overlap each other in the transport direction. That is, each spiral continuous groove formed in the width direction is represented by at least C in FIG. 2 with a spiral continuous groove and another groove formed at a position shifted from the spiral continuous groove in the transport direction. It is preferable to have such a shared region. Even if the overlap is too large, the gap between the grooves is substantially too close, thereby deteriorating the releasability of the formed film.Moreover, as the distance increases, the mirror surface portion increases, so that the present invention No effect. The size of the overlap is preferably 20% or less as a ratio (C / D) of the length C of the overlap portion in the transport direction to the diameter D of the spiral.

In this way, a series of spiral grooves formed continuously in the width direction have at least a common area at positions shifted from each other in the transport direction, so that uniform peelability can be obtained over the entire surface. can get.

The depth of the groove can be measured from a film sample formed using an endless belt or a drum made of metal such as stainless steel. That is, the belt (drum) contact surface of the cast film sample is measured using a scanning probe microscope, for example, SPI3800N manufactured by Seiko Instruments Inc.

Next, a method of forming continuous grooves spirally cut in each width direction on a support such as an endless belt or a drum made of stainless steel for casting will be described in detail.

The surface of the belt made of stainless steel, which has been previously mirror-polished, is first polished to a solution obtained by dissolving a small amount (eg, 3 g / l) of bengara (ferric oxide powder) in a 2 to 3% aqueous nitric acid solution and dispersing it. Soaking the polishing pad attached to the belt and moving it in the width direction of the belt (while rotating the polishing cloth) while pressing the belt with a certain pressure with a polisher, the corrosion effect of stainless steel by acid A spiral groove can be formed on the surface of the belt by polishing with the particles. The rotation diameter of the polisher, the speed of movement, and the concentration of bengara particles as an abrasive are changed to adjust these so that an optimum groove is formed. If the amount of the abrasive is too large, the whole is uniformly polished and the effect of the present invention cannot be obtained. Therefore, the amount of the abrasive is, for example, about 0.1 to 0.3% based on the nitric acid. . In addition, regarding the depth of the groove, the pressing pressure of the polisher, the concentration of nitric acid,
In addition, the presence or absence of flowing water at the time of using a polisher and, in this case, a bengara are used, but it can be adjusted depending on the type (hardness) of particles used.

Table 1 shows that a spiral continuous groove having a spiral size of about 200 mm and a spiral pitch of about 6 mm formed on the surface of a stainless steel support (in this case, an endless belt) was formed by a polisher. By changing the pressing pressure and the nitric acid concentration to change the depth,
It is a table | surface which shows the result of having analyzed the peeling property at the time of peeling, and the amount of the deposit which adhered to the surface after repeating casting of the cellulose ester dope liquid for time.

In Table 1, ○ indicates that the film could be peeled smoothly when the film was peeled from the support. The amount of the precipitate was evaluated based on the following criteria.

[0042] Multi 300 [mu] g / m ² or more medium 100 [mu] g / m ² or more ~300μg / m less 100 [mu] g / m less than ² less than ²

[0043]

[Table 1]

As can be seen from Table 1, after the film was formed for a certain period of time, when the depth of the spiral groove was 15 nm or more, the releasability deteriorated and the amount of the precipitate attached to the surface was detected in a large amount. No difference was observed in the releasability of the other two types, but it was found that the amount of the precipitate attached to the surface increased as the depth of the groove increased.

Some of the helical grooves deeply processed have surface deformations due to deterioration of the releasability, and the surface of the film sample (the surface in close contact with the belt) is scanned with a scanning probe microscope (Seiko Ind. Co., Ltd.). Instrument S
PI3800N), as a result, there was a dent on the surface due to the protrusion-like deposit on the belt,
In particular, a large dent along the groove was remarkably confirmed.

In the present invention, the film is preferably a cellulose ester film. In order to produce a cellulose ester film, first, a cellulose ester is dissolved in an organic solvent to form a cellulose ester solution (dope), which is cast on the above-mentioned support and molded.

The cellulose ester used in the present invention is
It is obtained by using cellulose selected from linter pulp, wood pulp and kenaf pulp, and reacting it with acetic anhydride, propionic anhydride or butyric anhydride in a conventional manner. 0.5-3.0 cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate propionate butyrate. The cellulose ester according to the present invention preferably has an acetyl group substitution degree of at least 1.5 or more. The degree of substitution of the acyl group of the cellulose ester can be measured according to ASTM D-817-91. The molecular weight of these cellulose esters is 70,000 to 3 as a number average molecular weight.
The range of 00000 is preferable because the mechanical strength when formed into a film is strong. 80,000-200,0
00 is preferred. Usually, the cellulose ester is formed into flakes after the treatment such as washing with water after the reaction, and is used in the shape. The particle size is 0.05 to 2.0 m.
By setting the range of m, the solubility can be accelerated, which is preferable.

The flakes are dissolved in an organic solvent mainly composed of a good solvent for the cellulose ester flakes in a dissolving vessel with stirring to form a dope. The dissolution is carried out at normal pressure, below the boiling point of the main solvent, under pressure above the boiling point of the main solvent, JP-A-9-95544, JP-A-9-95557 or JP-A-9-95538. A method performed by a cooling dissolution method as described in JP-A-11-21379
There are various dissolving methods such as a method performed at a high pressure as described in Japanese Patent Application Laid-Open No. H10-260, 1988. After dissolution, the dope is filtered with a filter medium, defoamed, and sent to the next step by a pump. The concentration of the cellulose ester in the dope is about 10 to 35% by mass.

Organic solvents as good solvents for cellulose esters include methyl acetate, ethyl acetate, amyl acetate, ethyl formate, acetone, cyclohexanone, methyl acetoacetate, tetrahydrofuran, 1,3-dioxolan, and 4-methyl-1,3. -Dioxolan, 1,4-dioxane, 2,2,2-trifluoroethanol, 2,
2,3,3-hexafluoro-1-propanol, 1,
3-difluoro-2-propanol, 1,1,1,3,
3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1
-Propanol, nitroethane, 2-pyrrolidone, N-
Examples thereof include methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, methylene chloride, and bromopropane. Methyl acetate and methylene chloride are preferably used. However, due to recent environmental problems, non-chlorine organic solvents tend to be more preferable. It is preferable to use a lower alcohol such as methanol, ethanol, or butanol in combination with these organic solvents, because the solubility of the cellulose ester in the organic solvent can be improved and the viscosity of the dope can be reduced. Particularly, ethanol having a low boiling point and low toxicity is preferable.

By adding a plasticizer such as a phthalic acid ester and a phosphoric acid ester, and an additive such as an ultraviolet absorber, an antioxidant and a matting agent to the dope, a silver halide photographic light-sensitive material caused by a cellulose ester film can be obtained. And the performance of the liquid crystal image display device can be improved.

The plasticizer that can be used in the cellulose ester film is not particularly limited, but is preferably a phosphate ester (triphenyl phosphate, tricresyl phosphate, etc.) or a phthalate ester (diethyl phthalate dibutyl phthalate, di-2 -Ethylhexyl phthalate, etc.), glycolic acid esters (triacetin,
Tributyrin, butylphthalylbutyl glycolate) and the like. If necessary, two or more plasticizers may be used in combination. The amount of the plasticizer added to the cellulose ester is preferably 0.5 to 30% by mass, and particularly preferably 2 to 15% by mass.

It is preferable that the cellulose ester film contains an ultraviolet absorber. The ultraviolet absorber has an excellent ability to absorb ultraviolet light having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of the liquid crystal and has good liquid crystal display properties. From the viewpoint of the above, those having absorption of visible light having a wavelength of 400 nm or more as small as possible are preferably used. In particular, the transmittance at a wavelength of 370 nm needs to be 10% or less, preferably 5%.
Or less, more preferably 2% or less. In the present invention, examples of the ultraviolet absorber that can be used include oxybenzophenone-based compounds, benzotriazole-based compounds, salicylate-based compounds, benzophenone-based compounds, cyanoacrylate-based compounds, nickel complex-based compounds, and the like. Benzotriazole-based compounds with little coloring are preferred. However, they can be used without limitation. Two or more ultraviolet absorbers may be used. As a method of adding the ultraviolet absorber to the dope, the ultraviolet absorber may be added after dissolving the ultraviolet absorber in an organic solvent such as alcohol, methylene chloride, or dioxolane, or may be directly added to the dope composition. The amount of the ultraviolet absorber used is 0.5 to 20% by mass based on the cellulose ester.
Can be added in the range of 0.6 to 5.0% by mass, and particularly preferably 0.6 to 2.0% by mass. Further, the cellulose ester film preferably contains an antioxidant. As the antioxidant, hindered phenol-based compounds are preferably used. 1 ppm to 1.0% is preferable in proportion, and 10%
~ 1000 ppm is more preferred. The cellulose ester film preferably contains a fine particle matting agent. As the fine particle matting agent, for example, inorganic fine particles such as silicon dioxide, titanium dioxide, aluminum oxide, and zirconium oxide or crosslinked polymer fine particles may be contained. Is preferred. Among them, silicon dioxide is preferable because the haze of the film can be reduced. These additives may be added together with the cellulose ester or the solvent when preparing the cellulose ester solution, or may be added during or after the solution is prepared.

The method for producing a cellulose ester film of the present invention can be applied to a cellulose ester film having a thickness of 20 to 200 μm, and particularly preferably to a thin film having a thickness of 20 to 100 μm.

Next, the step of casting the dope on a metal support (endless belt or drum), the step of drying on the metal support and the step of peeling the web from the metal support will be described. In the casting step, a solution (dope) of a polymer to be molded (for example, the above-mentioned cellulose ester) is fed to a pressure die through a pressure-type fixed gear pump, and at the casting position, an endless metal belt or a rotating metal that moves infinitely. This is a step of casting a dope from a pressure die onto a metal support such as a drum.

The location where the dope comes out of the slit of the pressure die is called a die. The slit shape of the die can be adjusted.
A pressure die that can easily make the film thickness uniform is preferable. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the doping amount may be divided to form a plurality of layers. In order to adjust the film thickness, it is preferable to control the dope concentration, the amount of liquid sent from the pump, the slit gap of the die cap, the extrusion pressure of the die, the speed of the metal support, and the like so as to obtain a desired thickness. In the present invention, the dope film cast from the base is called a casting film.

The drying step on the metal support is a step of heating the web (hereinafter, the film after the casting film is dried on the metal support is called the web) on the support to evaporate the solvent. It is. To evaporate the solvent, there are a method in which heated air is blown from the web side and the back side of the support, a method in which heat is transferred from the back side of the support by a heating liquid, and a method in which heat is transferred from the front and back sides by radiant heat. A method of combining them is also preferable. In addition, if the thickness of the web is thin, drying is quick. The temperature of the metal support may be the same as a whole or different depending on the position. The peeling step is a step of evaporating the organic solvent on an endless metal support that moves infinitely, and peeling the web before the metal support makes one round, and then the web is sent to a drying step. The position at which the web is peeled off from the metal support is referred to as a peeling point, and the roll which assists peeling is referred to as a peeling roll. Although it depends on the thickness of the web, if the residual solvent amount of the web at the peeling point (the following formula) is too large, it is difficult to peel off. Conversely, if the web is sufficiently dried on the support and then peeled off, the web May be peeled off. Usually, when the amount of the residual solvent is 20 to 150% by mass, the web is peeled off. As a method of increasing the film forming speed (the film forming speed can be increased because the amount of the residual solvent is increased as much as possible), there is a gel casting method capable of separating even if the amount of the residual solvent is large. Examples of the method include a method in which a poor solvent for the cellulose ester is added to the dope, gelling is performed after casting the dope, and a method in which the temperature of the support is lowered to gelate. There is also a method of adding a metal salt to the dope. By gelling on the support to strengthen the film, peeling can be accelerated and the film forming speed can be increased. When the residual solvent amount is peeled at a larger point, the web is too soft, impairing the flatness at the time of peeling, or the horizontal step due to the peeling tension, the rubbing and the vertical stripes are easily generated,
The amount of residual solvent can be determined based on the balance between economic speed and quality. The residual solvent amount used in the present invention can be represented by the following equation.

Residual solvent amount (% by mass) = {(M−N) / N} × 100 Here, M is the mass of the web at an arbitrary point, and N is the state of M at 110 ° C. for 3 hours. It is the mass at the time.

Usually, when the metal support is a stainless steel belt, the stainless steel belt has two drums (one is a drive drum for transferring the stainless steel belt, and the other is a delicate control of the transfer direction of the stainless steel belt to reduce the tension. Tension drum). Further, on the back side of the stainless belt, there may be provided several back rolls for supporting the stainless belt so as not to be loosened. Also, the position where the dope is cast (the position where the casting film comes into contact with the stainless steel belt) is usually not determined at which position on the stainless steel belt, but it is located on the drive drum or slightly downstream from the drum. It is often located far away. 3 and 4 show a pressure die 4 for film casting, a first drum 2 for drive, and a second drum 2 for tension.
An endless stainless steel belt (metal support) 1 stretched by two drums of a drum 3 and a film casting apparatus having a belt position adjusting mechanism 5 for adjusting the tension of the stainless steel belt. A schematic view from the top and side is shown.

The cellulose ester film formed by the above production method has good releasability, has no unevenness in the horizontal step, and shows excellent productivity. The cellulose ester film of the present invention is used as a protective film for a polarizing plate. A polarizing plate useful for a liquid crystal display device exhibiting excellent optical characteristics can be obtained by laminating the above.

For use as a protective film for a polarizing plate,
For example, at least one surface of a cellulose ester film is processed so as to be able to be bonded to a polarizing film. Examples of the treatment include a process of saponifying the surface with an alkali solution, a process of coating an adhesive layer, and the like, and a surface saponification process with an alkali is preferable.

With respect to the surface saponification processing as the protective film for a polarizing plate of the present invention, one example of the saponification treatment conditions of a cellulose ester film is as follows.
of NaOH aqueous solution for about 30 to 150 seconds, washed with normal temperature water for about 30 to 60 seconds, neutralized with 1 to 5% by mass HCl for about 30 to 60 seconds, and then with normal temperature water for about 30 to 60 seconds. The condition is that it is washed with water for 2 seconds and dried at about 80 ° C., but is not limited thereto.

The polarizing film used for the polarizing plate of the liquid crystal display device is
For example, polyvinyl alcohol, an aqueous solution of a polyvinyl alcohol-based polymer such as an ethylene-vinyl alcohol copolymer is formed into a film, and the film is uniaxially stretched and dyed with iodine or a dichroic dye. A water-resistant treatment is carried out with a crosslinking agent such as

The polarizing plate is provided on at least one surface of the polarizing film.
The protective film for a polarizing plate which has been subjected to an alkali saponification treatment is formed by applying an adhesive solution and bonding the same. Examples of the adhesive solution include a polyvinyl alcohol-based adhesive solution such as a polyvinyl alcohol aqueous solution and a polyvinyl butyral solution, and a vinyl polymerized latex such as butyl acrylate. A completely saponified polyvinyl alcohol aqueous solution is preferable.

By using the polymer film thus produced as a protective film for a polarizing plate, a polarizing plate useful for a liquid crystal display device can be obtained and can be preferably used for an image display device such as a liquid crystal display device.

[0065]

According to the present invention, it is possible to provide a method for minimizing the accumulation of precipitates and the like on the surface of a support while maintaining good releasability, and stably producing a smooth film for a long period of time.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a state of surface microdeformation (irregularity) generated on a film surface when peelability is poor.

FIG. 2 is a diagram showing an example of a support in which a continuous spiral groove is formed on the surface of the support.

FIG. 3 is a schematic view of an apparatus for film casting.

FIG. 4 is a schematic view of an apparatus for film casting.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stainless belt (metal support) 2 First drum for drive 3 Second drum for tension 4 Pressure die 5 Belt position adjusting mechanism

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Claims (9)

[Claims] 1. A method for producing a film in which a polymer solution is cast on a support by molding, wherein a continuous spiral groove is provided on the surface of the support. 2. The method according to claim 1, wherein the support is an endless belt. 3. The method according to claim 1, wherein the support is a drum. 4. The maximum diameter of the spiral formed on the surface of the support is 5
The method for producing a film according to any one of claims 1 to 3, wherein the thickness is not more than 00 mm. 5. A continuous spiral groove formed on a surface of a support, wherein a distance (pitch) between adjacent grooves in a width direction of the support is 10 mm or less.
5. The method for producing a film according to any one of 4. 6. A plurality of spiral grooves continuously formed in the width direction are formed in the transport direction on the surface of the support, and the grooves formed at positions shifted in the transport direction have at least a common area with each other. The method for producing a film according to claim 1, wherein: 7. The method for producing a film according to claim 1, wherein the depth of the continuous spiral groove on the surface of the support is 1 to 5 nm. 8. The method according to claim 1, wherein the polymer solution is a cellulose ester solution, and the film thickness of the formed cellulose ester film is 20 to 200 μm.
The method for producing a film according to any one of the above items. 9. A protective film for a polarizing plate, comprising a cellulose ester film formed by the film production method according to claim 8.